Tribaloy T-400 is known as hard particles having high wear resistance which are based on cobalt forming a hard phase constituted mainly of a molybdenum silicide.
A powder of a Co-2.5Si-28Mo-8.5Cr alloy, which is a material comparable to Tribaloy T-400, has been used in large quantities as hard particles greatly contributing to the wear resistance of automotive-engine valve seats (hereinafter referred to simply as “valve seats”) in automotive engines operated under high load. Therefore, a lot of techniques have been proposed.
For example, patent document 1 discloses, for the purpose of dispersing a larger amount of a hard layer in a matrix without impairing wear resistance, strength, etc., a process for producing a wear-resistant sinter member which comprises compacting a raw powder containing a matrix-forming powder (iron, SUS316, SUS304, SUS310, or SUS430) and a hard-layer-forming powder (Co-28Mo-2.5Si-8Cr), followed by sintering the compact, in which, at least 90% by mass of the matrix-forming powder is a fine powder having a maximum particle diameter of 46 μm, and the proportion of the hard-layer-forming powder in the raw powder is 40-70% by mass.
Patent document 2 discloses, for the purpose of obtaining an iron-based sinter alloy material having excellent wear resistance, a process for producing a wear-resistant iron-based alloy material for valve seats, in which 100 parts by weight of an iron-based alloy powder composed of a pure iron powder, iron alloy powder, carbon powder, steel powder having a fine carbide deposit, and hard-particle powder (e.g., Cr—Mo—Co system or Ni—Cr—Mo—Co system) is mixed with 0.2-3.0 parts by weight of a solid lubricant powder (sulfide or fluoride) and/or 0.2-5.0 parts by weight of a stabilized oxide powder (Y2O3 or CeO2, which each is an oxide of a rare-earth element, or CaTiO3), and the resultant iron-based alloy powder is compacted and formed, followed by sintering the compact to obtain a sintered body.
Patent Document 1: JP-A-2007-107034
Patent Document 2: JP-A-2003-193173